This article presents a case study of the former Yugoslavia, focusing on the role of language in constructing collective identities and establishing ethnic boundaries in relation to political borders. After looking at the variable and frequently multiple language-identity links in the South Slavic world, it examines the part that Serbo-Croatian, the principal language of the region, has played in the life stories of successive states on Yugoslav territory. A survey of the main dialectological facts and historical developments is followed by tracing the alternating waves of softening and hardening ethnic and linguistic boundaries as a concomitant of attempts at unification and separation, mostly driven by different brands of nationalism. We see how the construction, destruction and reconstruction of states have been reflected in the destiny of Serbo-Croatian, which came to be manipulated as a weapon in the Yugoslav wars of succession. With the federation's demise it was officially split up into Serbian, Croatian, Bosnian and Montenegrin as distinct national languages, nevertheless remaining a viable linguistic entity. We finally glance at the current situation of the four newly independent states, where both languages and borders are mainly employed to divide rather than to connect. (Contains 15 notes and 1 figure.)